Аннотация:A mathematical model of debris flow dynamics is developed. A debris now is treated as a two-phase continuum flow including solid and fluid constituents. Depth averaged equations of mixture theory for mass and momentum conservation are written for each phase. A viscous interaction between solid and fluid constituents is taken into account. The fluid phase (water) is considered as viscous one. Classical earth pressure theory is applied to the solid phase (debris). The bed drag for the solid "skeleton" obeys Coulomb's law. The model equations are integrated numerically. Several series of numerical simulations to determine the structure and dynamic characteristics of flow were carried out. An effect of phase diffusion is revealed. The velocity of phase diffusion, as a difference between the phase velocity and the average velocity of flow, was calculated. The influence of extra lateral water inflow (brook) on the structure and dynamics of two-phase debris flow is studied.